Patent EA-001045-B1 (EA)
Title: Jack-up offshore platform with submerged tank and methods of installing and lowering the tank-container
Inventor: THOMAS PIERRE-ARMAND
IPC: E02B17/02
Filed: 1999-03-10
Abstract: 1. A jack-up platform comprising an upper floating body (10) displacable along support legs (12), mechanical means (18) of the leg (12) displacement and a submergible tank-container designed to rest on the sea bottom, characterized in that said tank-container (14) is provided with a lower hatch (26) permitting a contact with marine medium, wherein said tank-container forms a bell-shaped cavity adapted to form in its upper portion an air cushion (30), said tank-container is connected with the bottom ends of said legs (12) enabling to displace it towards the body (10) using said mechanical means (18) of the legs displacement, said mechanical means are adapted to apply efforts either to lower or to raise said tank-container on the surface. 2. The platform as claimed in claim 1, characterized in that comprises means (27, 27A) for injecting pressurized gas into said tank-container (14). 3. The platform as claimed in claim 1 or 2, characterized in that said tank-container comprises a base (20A), the area of which is at least equal to the area of the body (10), and at least one upper board (22), partially protecting the base (20A) and also protecting the body (10), when it is quite near the base (20A). 4. The platform as claimed in claim 3, characterized in that the board or each section of it is forms a part of said tank-container. 5. The platform as claimed in claim 3 or 4, characterized in that said tank-container (14) forms essentially polygonal, in particular triangle or rectangular, and said boards (22) are arranged along the main length of at least two sides of the tank-container (14). 6. The platform as claimed in any one of the preceding claims, characterized in that the lower hatch is provided with a valve (26). 7. The platform as claimed in any one of the preceding claims, characterized in that comprises at least one foot piece (16) for resting on the sea bottom, wherein said foot piece or each foot piece (16) is provided with retention means towards the bottom surface of the tank-container, such as locking elements, liberated, when the foundation (17) rests on the sea bottom to permit lifting of the tank-container, disconnected at least from one foot piece (16) 8. The platform as claimed in claim 7, characterized in that the area of the carrying structure of the tank-container (14) overlapped by said foot piece or each foot piece (16) is less half area of the total bottom surface of the tank-container carrying structure. 9. The platform as claimed in claim 7 or 8, characterized in that said foot piece or each foot piece (16) is arranged nearby the outer contour of the tank-container, while the central zone of the tank-container is free. 10. The platform as claimed in any one of claims 7 to 9, characterized in that the height of the foot piece or each foot piece (16) allows to maintain a clearance between the sea bottom and the zone of the bottom surface of the tank-container not overlapped by the foot piece. 11. The platform as claimed in any one of claims 7-10, characterized in that the disconnectable locking elements comprise a mechanical catch. 12. A method of installing a submergible tank-container of a jack-up platform as claimed in any one of claims 7 to 10, in which the tank-container is initially under the body (10), and said body (10) is afoat on the sea surface, characterized in that comprises the following steps: a) the tank-container (14) is communicated with sea water via the hatch (26) so that to establish equilibrium  between the air cushion (30) and water, wherein the tank-container withstands only its own weight; b) the support legs are gradually lowered towards the body (10), said body being constantly afoat, providing gradual flowing of water into the tank-container (14) via the lower hatch (26), maintaining the pressure in the tank-container (14) approximately equal to the hydrostatic pressure of the tank-container at a depth, and c) after installation the tank-container (14) on the sea bottom, the body is raised above the sea level by displacement of the body towards the support legs. 13. The method as claimed in claim 12, characterized in that prior to step b) of lowering the legs, gas is injected into the tank-container (14). 14. The method as claimed in any one of claims 12 or 13, characterized in that the volume of the air cushion is adapted so that during the step b) of lowering the support legs at the initial stage the displacement means (18) force the legs (12) to move downwards, and at the next stage said displacement means counteract the lowering of the legs (12), drawn downwards by the tank-container (14). 15. The method as claimed in any one of claims 12 to 14, characterized in that during step b) pauses are observed allowing to maintain equilibrium between the pressure inside the tank-container (14) and outside by water flowing into it. 16. The method of raising of the submergible tank-container as claimed in any one of claims 1 to 11, in which the tank-container (14) is initially on the sea bottom and the body is afoat on the sea surface, characterized in that comprises the following steps: a) the tank-container (14) is communicated with sea water via the hatch (26); b) an air cushion is pumped into the tank-container (14), wherein the pressure of the air cushion is equal to the hydrostatic pressure of the tank-container at a depth; c) the support legs are gradually raised towards the body (10), said body being constantly afoat, providing gradual flowing out of water from the tank-container (14) thus maintaining the pressure in the tank-container (14) approximately equal to the hydrostatic pressure of the tank-container (14) at a depth. 17. The method as claimed in claim 16, characterized in that prior to step b) of raising the legs, gas is injected into the tank-container (14). 18. The method as claimed in any one of claims 16 or 17, characterized in that the volume of the air cushion is adapted so that during the step b) of raising the support legs at the initial stage the displacement means (18) force the legs (12) to move upwards, and at the next stage said displacement means counteract the raising of the legs (12), drawn upwards by the tank-container (14). 19. The method as claimed in any one of claims 16-18, characterized in that at step b) of raising the support legs (12) pauses are observed to maintain equilibrium inside and outside the tank-container (14) by inflowing water.